After harvesting, grain is usually dried and stored until the market is favorable to its sale. Since grain is largely sold by weight, it becomes important to have the maximum allowable moisture content in the grain before it is sold. If the moisture is maximized, the seller receives more for the same harvest of grain due to the extra weight provided by water.
In order to permit high moisture content grain to be safely stored without risk of deterioration, temperature sensing systems currently use thermocouple wires with sensors every few feet. Such cable sensors detect spot temperature changes caused by moisture migration, insect infestation, foreign matter accumulation or bacterial or mold contamination. The sensor can either localize the problem so that it can be eliminated or allow an operator to cool the grain to avoid moisture loss by overheating.
The conventional thermocouple wires used in grain temperature sensing consist of a stranded steel strength member adjacent to a bundle of thermocouple wires coated with polyethylene to insulate them from the steel strength member. A nylon coating then encloses both the stranded steel member and the coated thermocouple wires. Such a system has disadvantages in that moisture can short out contacts; stripping the multiple coatings makes difficult the connecting of the wires to other components of the sensing system and greatly increases the difficulty in manufacturing cables having multiple levels of coatings.
Additionally, loading and unloading of grain bins produces tension and fatigue problems in the present cable system. Wires stretch and break, and the insulation between the steel strength member and conductive wires separates, resulting in short circuits.
Other prior art thermocouple cables using fiberglass bundles circumferentially dispersed around an axial bundle of thermocouple wires do not provide satisfactory results in grain temperature measuring where there is a constant load on the cables because the fiberglass creeps with time, thereby weakening the cable and making it unsuitable for continued use.
Another prior art thermocouple cable utilizes strands of steel circumferentially dispersed around an axial bundle of thermocouple wires. This system provides the needed strain bearing support, but has many disadvantages. The steel makes the cable much heavier than desired and requires very good insulation and careful handling to avoid cutting the insulation, resulting in a short-circuit. The cable is difficult to construct due to the quantities of the wires and insulation layers.